Fluid-pressure-operated motors

ABSTRACT

A FLUID PRESSURE POWERED MOTOR HAVING A RECIPROCATING PISTON MOVABLE IN THE MOTOR CHAMBER ACTUATED BY PRESSURE DIFFERENTIAL ACROSS THE PISTON, A PILOT VALVE OPERATED BY THE OUTPUT OF THE MOTOR WHICH DIRECTS PRESSURE ALTERNATELY TO OPPOSITE SIDES OF A PISTON OPERATED MAIN VALVE. THE MAIN VALVE IN TURN REVERSES THE DIRECTION OF THE PRESSURE DIFFERENTIAL ACROSS THE MOTOR PISTON WHICH IN TURN REVERSES DIRECTION MOVEMENT OF THE MOTOR PISTON.

United States Patent Inventors John Horace Gadd Sunningdale; Ruben lhdekel, London; Edmund Joseph Suruins, London, England Appl. No 799.455

Filed Feb. 14, I969 Patented June 28, 1971 Priority Feb. 16, 1968 Great Britain 7786/ 6} Assignee Trico Products Corporation,

9e .911S.-X.-..

FLUlD-PRESSURE-OPERATED MOTORS 10 Claims, 9 Drawing Figs.

US. Cl 91/239, 91/310,91/314 Int. Cl F011 15/04, F011 25/06 Field of Search 91/239, 236, 310, 314

[56] References Cited UNITED STATES PATENTS 1,905,133 4/1933 Bishop et al. 1. 91/236 2,443,894 6/1948 Craze 91/239 2,491,402 12/1949 Tucker 91/236 Primary Examiner- Paul E. Maslousky Attorney-E. H. Liss ABSTRACT: A fluid pressure powered motor having a reciprocating piston movable in the motor chamber actuated by pressure differential across the piston; a pilot valve operated by the output of the motor which directs pressure alternately to opposite sides of a piston operated main valve. The main valve in turn reverses the direction of the pressure differential across the motor piston which in turn reverses direction of movement of the motor piston.

PATENTEUJUNZBBYI 3,587,396

SHEET 1 OF 7 I nvenlor JOHN HORACE GA DD EDMUND JOlBEPH SUM/N3 RUBEN HADE/(EL PATENTEflJuuzszs'n 3.587.396

SHEET 2 OF 7 Inventor JOHN HORACE GADD EDMUND JOSEPH SUM/N3 RUBEN JADE/(6L PATENTEU JUN28 I97! SHEET 3 OF 7 lnvenlor JOHN HORACE G-ADD EDMUND JOSEPH SUM/N5 RUBEN HA DE/(EL PATENTEnJuuzslsn 3,587,396

SHEET 0F 7 .lnvenlor JOHN HORACE GAUD EDMUND JOSEPH 5UMIN$ RUBEN HADEHEL PATENTEUJUNZBIQYI 3,587,396

SHEET 5 OF 7 lnvenlor JOHN HORACE GADD EDMUND JOSEPH SUM/N5 B IQUBE/V [JADE/{EL A Horne y PATENIED JUH28 m?! SHEET 6 BF 7 A llorney PATENTED JUN28 m1 SHEET 7 OF 7 lnvenlor JOHN HORACE GADD EDMUND UOSEPH SUM/N5 By RUBEN [JADE/(EC A Home y FLUID-PRESSURE-OPERATED MOTORS BACKGROUND OF THE INVENTION The invention relates to fluid pressure motors and more particularly to fluid pressure motors for driving windshield wipers.

Existing pneumatic wiper motors suffer from a number of shortcomings, the first of which is a tendency to give somewhat sharp reversal at the end ofeach motor stroke. This can be controlled to some extent by throttling the flow of air into or out of the motor, but only at the expense of slowing down the overall motor speed to a point where it may not be feasible to obtain a combination of adequate speed of operation and adequate smooth reversal. Furthermore, such throt' tling is somewhat wasteful of pressure.

A further shortcoming of existing motors lies in the arrange ments currently provided to give automatic parking, and in many cases no automatic parking is provided. A desirable automatic parking system is one in which the motor parks automatically when the dashboard control is moved to Off," since this gives the simplest possible control sequence. A further requirement in many cases is that when the motor is parked, air supplied to the internal parts should be shut off to prevent fluid pressure losses through leakage. It is also desirable that there be a minimum-number of air lines between the dash board control and the motor in order to facilitate installation. Current methods of insuring parking of air motors fail to achieve all these objectives simultaneously.

SUMMARY OF THE INVENTION The motor of the present invention provides a smooth reversal by utilization-of parallel restricted fluid passages between the main valve and an exhaust port. One of these passages flows through the pilot valve which is responsive to motor piston movement. The pilot valve is arranged to close the passage flowing therethrough at the end of a motor stroke and to reopen the passage at the beginning of the next stroke so that the motor slows down only near the end of a stroke to accomplish this smooth reversal. The parking feature obtained by use of a manually operable control member, movable between a first position which causes the motor to operate and a second position which causes the motor piston to stop at the end of a stroke in a predetermined direction and further valve means actuated by the control member and arranged so that all movement of the control member to the second position, then, according to the direction of movement of the motor at that time, either the main valve is held in a condition such that the motor member will complete a stroke in the predetermined direction and will then stop, or the main valve is moved to that condition at the end of a stroke opposite to the predetermined direction, and it is thereafter held in that direction.

A principal object of the present invention is to provide a smooth reversal of the motor without excessive interferences at an average speed of the motor.

Another object of the invention is to provide an automatic parking system which causes the motor to stop at the end ofa stroke in a predetermined position, regardless of the position of the piston, at the time the manual control is placed in the off position.

Other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the moving parts of the motor in the parked position;

FIG. 1A is an exploded detail;

FIG. 2 is a vertical section through the motor, on the axis of its output shaft;

FIG. 2A is a fragmentary horizontal section, on the axis of the motor output shaft; and

FIGS. 3 to 7 are diagrams of the motor and a control, in various positions during a cycle.

The motor comprises a housing containing a cylinder 1 in which slides a piston 2. The piston 2 carries a rack 5 which meshes with a pinion 6, fixed on a hollow shaft 60 which forms the motor output. In use, an inner shaft 72 (FIG. 2), carrying a driving crank arm 73, is inserted into the hollow shaft 6a, and locked to it. The motor has a parked position, so that if the motor is used to drive one or more wipers for a vehicle windscreen through a suitable transmission, the wipers will be parked when the motor is in its parked position.

The parked position is fixed, and is with the piston to the right, FIGS. I and 3. The location of the opposite extreme position of reciprocation of the piston may be varied to vary the arc of wipe of the wiper or wipers.

As shown in FIG. 3, the piston 2 divides the cylinder 1 into chambers 3 and 4. Preferably, as shown in FIG. 2, the rack and the pinion are inside the housing 67, the shaft 60 extending from the housing in fluidtight manner, through rotary seals 70, 71.

The output shaft 6a carries a valve actuating striker 7 fixed to it, and a second striker 8, FIGS. 1 and 2, which can be adjusted angularly in relation to the striker 7, to vary the arc of wipe.

The shaft 6a is formed with a peripheral recess 9 (FIG. 3) capable of receiving a locking latch 10 formed on a lever 11 pivoted at 12, and urged into engagement with the shaft by a spring 13.

The strikers 7, 8 operate a valve'driving member 14 fixed to a shaft 15 which enters a valve chamber 16 (FIG. 2A) through a seal 16a. The striker 7 operates the member 14 as the piston 2 goes towards the right extreme position, and the striker 8 operates the member 14 as the piston goes towards the left extreme position. Through this description, references to directions, such as right" left" up down, are to directions as seen in FIG. I and FIGS. 3 to 7.

In the preferred arrangement, as shown, the valve operation is in two stages (described below), spread over an appreciable angular travel of the shaft 60. For this reason, each striker has two one-sided teeth, 18, 19 and 22, 23 respectively (FIG. 3), which transmit drive successively. The teeth are staggered in the axial direction so that on reversal of movement of the shaft 611 the teeth disengage from the cooperating teeth 20, 24 or 24, 21 on the valve driving member 14, which are likewise staggered, the teeth 20 and 21 being one-sided and the tooth 24 double-sided. Hence the movement of the member 14 and shaft 15 does not reverse until towards the end of each stroke. The teeth on each striker are duplicated at the opposite end of a diameter. This enables an alternative spacing between the teeth 18 and I9, and between the teeth 22 and 23 so as to give a different period of slowing down at the end of each stroke, as circumstances may require.

Three valve chambers 16, 17, 17a (FIGS. 2 and 2A) are connected to air under pressure from a suitable source when the motor is working, as explained hereunder. The chambers 16, 17, 17a contain valve members 25, 26 and 27 which can slide or turn on a flat face 28 in which valve ports open, so that when any port is unmasked by a valve it is connected to pressure. The source of air pressure may be a compressor driven by the vehicle engine. The flat face 28 is one side of a plate 66 which is fixed to the housing 67. A gasket 68 is interposed. Various passages which lie in the plate 28 and the housing 67 and are connected to the ports in the face 28 are indicated in the diagrammatic FIGS. 3 to 7, but are omitted from FIGS. 2 and 2A to avoid confusion. The valve chambers 16, 17, 17a are formed in a cover 66a, 66b fixed to the plate 66 and the housing 67. The three chambers are interconnected by passages (not shown). In FIG. 1 only the outline of the housing 67, plate 66 and cover 66a, 66b is indicated, at 69.

The valve member 25 is part of a pilot valve 250, driven by the shaft 15.

The valve member 26 is part of a main valve 26a, driven by pistons 29, 29a controlled by the combined action of the valve 25a and of a starting valve 27a.

The valve member 27 is part of the starting valve 270, under the control of an auxiliary piston 30 moving in a cylinder 31 formed in the cover 66a adjacent to the valve chamber 17, a chamber 32 of the cylinder 31 being connected to the source of pressure through a port 33. The piston 30 is connected to a rod 34 moving within the valve chamber 17. The rod 34 protrudes through a seal from the chamber 17, and its end 36 operates the locking lever-11.

The piston 30 'is operated by a remote-control valve 37 (FIG. 3), mounted where it can be operated by the driver of the vehicle, e.g., on the dashboard. The valve 37 has an operating knob 37a, and in FIG. 3 is shown in the off position, the right side of the piston 30 then being connected to exhaust through a port 38a,'a pipe 38b, a port 38, and a restrictor 39. Pressure in the chamber 32 then holds the piston 30 to the right. A shoulder 40 on the rod 34 then acts as a valve member in cooperation with a seat 41, thus sealing off the chambers 16,17,17a from the chamber 32. The pressure connection 33 is thus then sealed off by the piston 30 and the valve 40/41, thus preventing air losses through internal leakage when the motor is not running, which could otherwise be significant over long periods.

The motor is set to run by reversing the position of the valve 37, as shown in chain lines in FIG. 3. In the on" position, the right side of the piston 30 is connected through a port 42 and a restrictor 43 to a separate pipe 430 leading to the supply of air pressure. This causes the piston 30 to move to the left, by reason of the excess area of the right face as compared with the left face of the piston. The exhaust port 38 in the valve 37 is closed. As soon as the piston 30 begins to move, as indicated in chain lines in FIG. 3, pressure is admitted to the interconnected chambers 16,17, 17a past the seat 41. As explained later, the motor begins to run as the piston 30 reaches the left end of its travel. Whilst the rod 34 is moving, the restrictor 43 limits its speed (say about one-half second for full stroke), and this has two effects:

a. In the configuration of FIG. 3, the chamber 3 to the left of the piston 2 becomes connected to pressure, as explained later. Pressure is likely to have leaked away while the motor was parked. The time delay given by the restrictor 43 allows pressure to build up in the chamber 3 before the first leftward stroke 'of the piston 2. This tends to move the piston 2 to the right, which relieves the load on the latch which can then be disengaged easily from the recess 9 by the piston 30 as it travels to the left. The spring 13 is very light.

b. The buildup of pressure in the chamber 3 allows the governing system described later to come into effect immediately, i.e., during the first stroke of the piston 2 to the left.

The starting valve member 27 is a disc pivoted on a central axis, and actuated by two projections 44a and 44b (FIG. 1A) 0n the back of the disc, which cooperate with cam surfaces 49a, 49b on a block '48 carried by the rod 34. In the parked condition, the valve member 27 is held in an anticlockwise position. As the piston moves to the left, the disc does not move until the piston has travelled about half its stroke. Then during the remainder of the stroke the valve member 27 is turned progressively clockwise.

In the parked condition (FIG. 3, solid lines) the right-hand side of the piston 29a is connected to pressure through a port 50 through the surface 28 and not covered by the valve member 27, while the left-hand side of the piston 29 is connected to exhaust through ports 51, 52 in the starting valve 2711. Throughout FIGS. 3 to 7, to avoid many broken lines, the ports, and the grooves in the valve members 25, 26, 27, are shown in solid lines, although they in fact lie on the far faces of the valve members. There is a recess 50a opening to the side of the valve member 27.

The connection from the piston 29 to exhaust through the valve 27a is not essential, but is a safety measure. Its purpose is as follows: the main valve member 26 ends up to the left as the motor goes to parked position, as will appear later. In the off" condition, when pressure is cut off from the valve chambers 16, 17, 17a, it is conceivable that vibration could cause the valve member 26 to move to the right, thus resulting in an incorrect starting position of this valve member. The connections as shown ensure that, the moment pressure is admitted to the valve chamber 17a, the valve member 26 will move to the left if it has drifted away from its lefbhand position due to any cause, thus resulting in a correct starting position.

As the starting valve member 27 moves towards the position shown in FIG. 4, the port 51 is connected to a port 53 in the valve 27a and thence to a port 54 in the valve 25a. The port 54 is in communication with the valve chamber 16. The left-hand side of the piston 29 is thus connected then to pressure, and the valve member 26 is in balance. It will therefore stay at the left.

When the starting valve member 27 reaches the position shown in FIG. 4, a port 50 is connected to a port 55 in the valve 27a and hence to a port 56 in the valve 251:, and hence to exhaust through a port 57. The right-hand side of the piston 29a is thus now connected to exhaust, and the main valve member 26 moves to the right.

With the starting valve member 27 in the position of FIG. 4, the motor is in the run condition, ports 54, 56 in the pilot valve 250 being connected (through the valve 27a) respectively to the leftand right-hand sides of the pistons 29, 29a. Thus, the left-hand side of piston 29 is connected to pressure and the right-hand side of piston 29a is connected to exhaust. Therefore, the valve member 26 moves to the right exposing port 600. The valve chamber 17 is pressurized through port 33, chamber 32 and the port through valve seat 41 of valve 27a. With the pistons 29, 29a in the position shown in FIG. 4, valve 26 exposes port 600 which is in fluid communication with chamber 4 to the right of main piston 2 of motor cylinder 1. Chamber 3 to the left of main piston 2 is ported to exhaust through ports 58 and 59 in valve 26a, thence through restrictor 60 and also through ports 58 and 61 in valve 26a, thence through ports 62 and 63 in pilot valve 25a and through restrictor 64. Thus, main piston 2 moves to the left. As the piston 2 approaches the left-hand end of its travel, the pilot valve member 25 moves anticlockwise to the position shown in FIG. 6 as explained later, in which position the connections to ports 54 and 56 are reversed. With the valve 25a in the position shown in FIG. 6, port 56 is opened and exposed to pressure; it communicates with port 55 of valve 27a, thence through port 50 to the chamber at the right-hand side of piston 29a. The chamber at the left-hand side of piston 29 in valve 26a is exhausted through port 51 of valve 27a, thence to port 53 to valve 25a, through ports 54 and 57 to exhaust. The main valve member 26 will therefore reverse, moving again to the left as shown in FIG. 6. With the valve member 26 of the main valve 26a moved to the left as shown in FIG. 6, port 58 is opened and exposed to the pressurized chamber 17. Port 58 is in com munication and conducts pressurized fluid to chamber 3 of main cylinder 1 to the left of piston 2. Chamber 4 to the right of main piston 2 is then exhausted through ports 60a and 60b of main valve 26a, thence to ports 60c and 63 of pilot valve 25a and thence to exhaust through restrictor 64. Simultaneously chamber 4 to the right of main piston 2 in cylinder 1 is exhausted through ports 60a and 50 through restrictor 60. Thus the main piston 2 moves to the right. The main valve member 26 will reverse again to the right as the piston 2 approaches the right-hand end of its travel and again to the left as the piston 2 approaches the left-hand end of its travel, and so on. Thus the piston 2 is caused to reciprocate.

As the valve member 26 moves to the right to the position of FIG. 4, the chamber 3 of the main cylinder 1 is connected to exhaust through ports 58, 59 in the main valve 26a and a restrictor 60, and simultaneously through a port 61 in the main valve 26a, ports 62, 63 in the pilot valve 25a and a restrictor 64. The restrictors 60 and 64 in parallel then limit the speed ofthe main piston 2 to the left.

At an appropriate point of the stroke of the piston 2 to the left, the teeth 22, 21 engage and bring the pilot valve member 25 to the position shown in FIG. 5. The port 61 is then cut off from the port 63, and the chamber 3 can exhaust only through the ports 58, 59 and the restrictor 60, the latter being small enough to cause substantial slowing down of the piston 2, towards the end of'its stroke to the left, thus helping to ensure smooth reversal.

As the piston 2 nears the end of its stroke to the left, the teeth 23, 24 engage and bring the pilot valve member 25 to the position shown in FIG. 6,-so causing the main valve member 26 to reverse. In this position the chamber 4 exhausts through the ports 60a, 59 and the restrictor 60 and through the ports 60a, 60b, 60c, 63 and the restrictor 64.

A similar sequence is obtained when the piston 2 moves to the right. In this case the member 14 is driven by the striker 7 instead of the striker 8.

Thus the main piston 2 reciprocates, its speed over the main portion of each stroke being governed by the resistance of the restrictors 60 and 64 in parallel, and its speed near the end of each stroke being governed by the restrictor 60 alone, and hence considerably reduced.

When the control valve 37 is manually returned to the off position, as shown in FIG. 7, the right side of the cylinder 31 exhausts through the restrictor 39, and the pressure in the chamber 32, fromv the supply 33, urges the piston 30 to the right. The restrictor 39 limits the speed of the piston (say about 2 seconds for full stroke).

In the initial movement of the piston 30 to the right, the starter valve member 27 moves from the position of FIGS. 4, 5 and 6 to that of-FIG. 7, disconnecting the port 50 from the port 55 and then connecting the port 50 to the pressure in the chamber 17a. Pressure is thus connected to the right-hand side of the piston 29a. The consequence of this depends on whether the main valve member 26 is at that moment to the left or to the right. If, as shown, the main valve member 26 is to the left, with the main piston 2 moving to the right, then the effect is to prevent any further reversal. The left'hand side of the piston 29 is still connected to exhaust via the port 57 and the port 54 in the valve 25a and the ports 53, 5] in the starter valve 270, which remains in the position of FIG. 7 long enough for the parking cycle (as described hereunder) to be completed.

As the main piston 2 approaches the end of its stroke to the right, and the pilot valve member 25 is brought to the position shown in FIG. 3, the starter valve member 27 being still in the position of FIG. 7, and the main valve member 26 then being to the left, pressure is applied to both sides of the pistons 29, 29a, to the left from the port 54 in the valve 25a via the ports 51,53 in the valve 27a, and to the right from the port 50 in the valve 27a. The pistons 29, 29a are thus in balance, and do not move, and the main valve member 26 stays over to the left. The main piston 2 thus continues its stroke to the right and stops against the end wall of the cylinder.

If, at the time of movement of the starter valve member to the position of FIG. 7, the main valve member 26 is to the right, with the main piston 2 moving to the left, as in FIG. 4, then the effect is to permit one further reversal under the control of the pilot valve 25a. The left-hand side of the piston 29 is under pressure. Putting the right-hand side of the piston 29a under pressure merely balances the main valve member 26, but does not move it. When the main piston 2 completes its stroke to the left, the pilot valve 25a cuts off the left-hand side ofthe piston 29 from pressure and connects it to exhaust, as in FIGS. 5 and 6. Thereupon the main valve member 26 moves to the left and remains there. The main piston 2 then makes a stroke to the right, and stops, as described above.

As the auxiliary piston 30 moves to the right, beyond the position of FIG. 7 to that of FIG. 3, eventually the latch engages the recess 9 in the shaft 6a. This mechanical lock is desirable for some installations with wipers mounted adjacent to the upper edge of the windscreen, to prevent the wipers dropping under the action of gravity when the motor is in the parked position, and also some installations with wipers mounted adjacent to the bottom edge of the windscreen which may incorporate a spring providing a bias away from the parked position.

During the latter half of the stroke of the auxiliary piston 30 to the right, the projection 44a, and the cam surface 49a bring the starting valve member 27 back from the position of FIG. 7 to the position of FIG. 3. This has no effect apart from correcting possible drift of the main valve member 26 before the motor is again set to run," as described earlier. As the piston 30 gets to the end of its stroke to the right, the shoulder contacts the seat 41, and pressure is cut off, as explained earlier.

The restrictors 60, 64 may be adjustable so that the rate of acceleration and deceleration of the motor piston 2 can be controlled, but this is not essential. Once a suitable setting has been achieved, a restrictor fixed at that setting could be used. In the example shown, the restrictors are holes in a disc indicated at 65, which can easily be exchanged for another, to suit the inertia of the wiping system of a particular vehicle. The restrictor 64 may be omitted.

The restrictors 39 and 43 could be replaced by a single restrictor in the pipe 38b. Separate restrictors enable separate selection of the times taken by the auxiliary piston 30 to move to the left and to the right.

Certain specific embodiments of the invention have been described for the purpose ofillustration but it will be apparent that various other modifications andl other embodiments are possible within the scope of the invention. For example, in accordance with the broader aspects of the invention the motor, through described as using air pressure, may use hydraulic pressure, the exhaust flows being returned to a reservoir.

The motor could also be powered by vacuum. A motor having an oscillating vane in place of a reciprocating piston could be employed, the vane being fixed directly to the output shaft. The motor, though described as being used in connection with windshield wipers, could be used for other and different pur poses as, for example, to drive a paint mixing machine or an artificial lung machine.

It is to be understood, therefore, that the invention is not limited to the specific arrangement shown, but in its broadest aspects it includes all equivalent embodiments and modifications which come within the scope ofthe invention.

We claim: 1. A fluid-pressure-operated claim: having a motor chamber and a motor member movable to and fro by fluid pressure difference, pilot valve means responsive to the movement of the member to operate a main valve by fluid pressure difference and thereby reverse the member at the end of each stroke, and first and second connections in parallel between the main valve and one fluid pressure, the first connection passing through a restriction, and the second passing through the pilot valve means, which is arranged to close the second connection as the motor member approaches the end of each stroke, and to reopen the second connection at the beginning of the next stroke.

2. A motor according to claim 1, in which the second connection passes through a second restriction.

3. A motor according to claim 1., including a manually operable control member movable between a first position which causes the motor to operate and a second position which causes the motor member to stop at the end of a stroke in a predetermined direction, and further valve means, actuated by the control member and arranged so that, on movement of the control member to the second position then, according to the direction of movement of the motor at that time, either the main valve is held in a condition such that the motor member will complete a stroke in the predetermined direction and will then stop, or the main valve is moved to that condition at the end ofa stroke opposite to the predetermined direction and is thereafter held in that condition.

4. A fluid-pressureoperated motor having a motor chamber and a motor member movable to and fro by fluid pressure difference, pilot valve means responsive to the movement of the member to operate a main valve by fluid pressure difference and thereby reverse the member at the end of each stroke, a manually operable control member movable between a first position which causes the motor to operate and a second position which causes'the motor member to stop at the end of a stroke in a predetermined direction, and further valve means, actuated by the control member and arranged so that, on movement of the control member to the second position, then, according to the direction of movement ofthe motor member at that time, either the main valve is held in a condition such that the motor member will complete a stroke in the predetermined direction and will then stop, or the main valve is moved to that condition at the end of a stroke opposite to the predetermined direction and is thereafter held in that condition.

5. A motor according to claim 4, in which the further valve means alternatively connects an operating chamber in the main valve to a passage; controlled by the pilot valve or to a passage connected to one pressure.

6. A motor according to claim 5, in which the further valve means alternatively connects an opposite operating chamber in the main valve to a passage controlled by the pilot valve, or to a passage connected to a second pressure, different from the said one pressure.

7. A motor according to claim 4, in which the further valve means is actuated by a member which is movable to and fro, and that member, at an extreme position, attained in response to movement of the control member to its second position, cuts off the pilot valve means and the main valve from a source of nonatmospheric pressure.

8. A motor according to claim 4, in which there is a springloaded latch which, when the motor is stopped, engages and locks a component coupled to the motor member, and the further valve means is actuated by a member which is movable to and fro, and that member, at an extreme position, attained in response to movement of the control member to its first position, displaces the latch from locking position.

9. A motor according to claim 4, in which the further valve means is actuated by a further motor member which is movable to and fro by a fluid pressure difference, and the control member is arranged to actuate a valve which alters this pressure difference, the speed of movement of this further motor member upon movement of the control member to this second position being limited by a restriction in a fluid flow passage.

10. A motor according to claim 9, in which the speed of movement of the further motor member upon movement of the control member to its first position is also limited, by a restriction in a fluid flow passage.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 587 396 Dated June 28 1971 Inventor(s) John Horace Gadd, et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 6, line 40 should read "We claim:"; line 41 should read "1. A fluid-pressure-operated motor having a" Signed and sealed this 21st day of March 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD M.F'LETCHER, JR.

Commissioner of. Patents Attesting; Officer FORM PO-105O (10-59) USCOM'WDC Bo375 pe9 w u s covznnmzm- PRINTING ornc: I969 0-366-33 

